The invention is based on a priority application EP 02360138.8 which is hereby incorporated by reference.
The invention relates to a (de-)interleaver circuit for (de-) interleaving optical signals. The invention further relates to a method of interleaving a first and a second optical signal each having a plurality of multiplexed channels of light, and a method of de-interleaving an optical signal having a plurality of interleaved multiplexed channels of light.
Optical Wavelength Division Multiplexing (WDM) and Dense Wavelength Division Multiplexing (DWDM) are commonly employed technologies in optical transmission systems as means to use available resources more efficiently. In WDM and DWDM transmission systems, multiple optical signals are simultaneously transmitted over a single optical fiber. Each signal is generated from a carrier signal having a pre-allocated carrier wavelength. At a transmitter end, the carrier signals are usually amplitude modulated by digital information signals. Due to the different carrier wavelength, the signals transmitted in the optical fiber do not substantially interfere with each other. At a receiver end, the signals with different wavelengths are separated by narrow band filters and then detected or used for further processing.
In such systems, each signal is, mainly due to the modulation, not transmitted with only a single wavelength but within a narrow wavelength band that is centered around a so-called center wavelength. Such a band is also referred to as an optical channel. Each channel is therefor characterized by a single center wavelength. In practice, the number of channels that can be carried by a single optical fiber in a WDM or DWDM system is limited by crosstalk, narrow operating bandwidth of optical amplifiers and/or optical fiber non-linearities.
Currently, internationally agreed upon channel spacing for high-speed optical transmission systems is 100 GHz, equivalent to 0.8 nm spacing between center wavelengths of adjacent channels. However, recent research activities focus on systems having 40 channels with only 50 GHz channel spacing.
Such channel spacings in high-speed WDM and DWDM systems can be achieved with components referred to generically as optical interleavers. An interleaver is a multiplexer that takes optical signals of different channels from two or more different input ports and combines them so that they may be coupled to an output port for transmission over a single optical fiber. A de-interleaver is a de-multiplexer that divides a signal containing two or more different channels according to their wavelength bands and directs each channel to a different dedicated fiber. A de-interleaver can also be used as a router that can, according to control signals, selectively direct each channel to a desired coupling between an input channel and an output port.
The general principle behind (de-)interleavers is an interferometric overlap of multiple beams. The devices exploit the physical effect that interference creates a periodically repeating output (fringes) as different integral multiples of wavelengths pass through the device. Since the path of light is generally reversible, the same device may be used as an interleaver or a de-interleaver, depending on the port(s) into which light is coupled to.